1. Field of the Invention
The present invention relates to an industrially advantageous novel process for producing a metal phthalocyanine and/or its derivative (hereinafter sometimes referred to simply as metal phthalocyanines).
2. Discussion of Background
Metal phthalocyanines are pigments which are most important from the industrial point of view. Among them, copper phthalocyanines have beautiful blue colors and excellent properties such as heat resistance, chemical resistance and light resistance, and they are widely used in the field of coating materials, printing inks or resin coloring agents, mainly as blue pigments. In the following description, such copper phthalocyanines will be used as typical example for detailed description.
A number of methods have been proposed for the preparation of copper phthalocyanines. Among them, a so-called phthalodinitrile method and a phthalic anhydride-urea method (hereinafter referred to simply as a urea method) are industrially important. It is common to employ the urea method for the preparation of copper phthalocyanines in a large amount on an industrial scale.
The urea method is a method wherein phthalic anhydride, phthalic acid or its derivative and urea, a copper compound and a catalyst are heated in the presence of an organic solvent. As the derivative of phthalic acid, an ammonium salt of phthalic acid, phthalimide, a phthalic acid ester, a phthalic acid amide or orthocyanobenzoic acid may be mentioned. Such phthalic anhydride, phthalic acid or its derivatives may be used alone or in combination as a mixture of two or more.
As the nitrogen source for copper phthalocyanines, ammonia and biuret are known in addition to urea. However, industrially, urea is mainly used. In literatures such as patents, cyanuric acid is usually disclosed as this nitrogen source. However, there has been no instance wherein a metal phthalocyanine is prepared by using cyanuric acid. In fact, according to the experiments by the present inventors, cyanuric acid does not function as the nitrogen source in the reaction of this type.
As the copper compound, copper halide such as cuprous chloride is most commonly used industrially. However, a metal copper, copper oxide, copper cyanide, copper sulfate, copper nitrate and copper acetate may also be employed for this purpose. The amount of the copper compound is most advantageously at a level of 1 mol per 4 mol of phthalic anhydride from the viewpoint of yield. Use of the copper compound in an excess amount not only brings about a reduction in the yield but also is industrially disadvantageous from the viewpoint of environmental pollution due to an increase of copper ions discharged into a waste water from the purification.
As the catalyst, a molybdenum compound such as ammonium molybdate, molybdic acid, phosphorus molybdic acid, ammonium phosphorus molybdate or molybdenum oxide. Among them, ammonium molybdate is particularly superior. In addition to the above, arsenic vanadium compound, boric acid or a halide or an oxyhalide of titanium, tin or antimony, may be used.
As the solvent for the reaction of the urea method, an inexpensive organic solvent which is thermally stable and not reactive with the reaction product during the reaction and which is liquid at room temperature and has a narrow range of the boiling point within a range of from 170.degree. to 240.degree. C. and low toxicity is suitable for industrial purpose. Heretofore, trichlorobenzene or nitrobenzene has been used for an industrial operation as a solvent which substantially satisfies such conditions. However, these solvents are disfavored because of the toxicity and possible environmental polution, and recently, alkylbenzenes are favorably employed for industrial purpose.
The mechanism for the formation of copper phthalocyanines in such a urea method has not yet been completely understood. However, there are the following problems from the viewpoint of phenomena observed during the reaction for the formation of phthalocyanine.
Phthalic anhydride used as one of the main starting materials for the synthesis of copper phthalocyanine, can readily be converted to phthalimide by contacting it with ammonia gas at a temperature of at least 170.degree. C. Therefore, it has been industrially common to convert phthalic anhydride to the imide with ammonia gas preliminarily generated by the reaction, to save the consumption of urea. Accordingly, in the reaction for the formation of copper phthalocyanine by the urea method, even if phthalic anhydride is used, the starting substance is believed to be phthalimide. At the initial stage of the reaction for the formation of copper phthalocyanine, when the reaction system is heated to a temperature of at least the melting point of urea, firstly the copper compound (mainly cuprous chloride) and the catalyst molybdenum compound are dissolved in molten urea, and this urea-cuprous chloride-molybdenum compound melt is reacted with phthalimide to form yellowish brown intermediate I. As the heating is continued at a temperature of at least 170.degree. C., it turns into reddish brown intermediate II. As the heating is further continued, formation of copper phthalocyanine III starts to take place.
Thus, the phthalocyanine-forming reaction contains the above-mentioned three steps as the phenomena. Phthalimide has fairly good solubility in an organic solvent at a temperature of at least 170.degree. C. when used alone. However, when it is present together with a melt of urea-cuprous chloride-molybdenum compound, phthalimide transfers from the organic solvent phase to the molten phase of the urea-cuprous chloride-molybdenum compound and reacts to form copper phthalocyanine through the above-mentioned three steps. Thus, the copper phthalocyanine-forming reaction proceeds in urea, i.e. proceeds in a phase different from the organic solvent. At the initial stage of the reaction, urea is present in an adequate amount in the liquid state and thus serves as a solvent, whereby the reaction proceeds in the urea solvent. However, as the reaction progresses, urea is consumed by the reaction, and its amount decreases as time passes and finally it will not function as the solvent. The organic solvent provides no substantial solubility to the reaction product. Therefore, when urea is consumed by the reaction and is no longer substantially present as liquid, the reaction product will be present in the form of solid in a different phase in the organic solvent. In this state, copper phthalocyanine is formed via the above-mentioned three steps. When urea has been consumed by the reaction and no longer functions as a solvent, the fluidity of the reaction product becomes poor, the reaction solution becomes rapidly viscous and the torque exerted to stirring vanes rapidly increases. In spite of forcible stirring with a clearance with the inner wall of the reaction tube set to be as small as possible by means of anchor-type stirring vanes, the moving (rotational) speed of the reaction product in contact with the inner wall of the reaction tube drops to a level of not higher than 1/100 of the rotational speed of the stirring vanes, and the reaction product does not substantially move.
The degree of the torque during the stirring of this reaction solution varies depending upon the organic solvent used. When three solvents of nitrobenzene, trichlorobenzene and an alkylbenzene which are most commonly used as organic solvents for the reaction for the synthesis of copper phthalocyanine are compared, the degree of the increase of the torque is in the order of the alkylbenzene&gt;&gt;trichlorobenzene&gt;nitrobenzene. Thus, the torque is greatest in the case of the alkylbenzene which is most widely used on an industrial scale as a solvent which is safe and harmless from the viewpoint of food hygiene and environmental hygiene.
The decrease of the fluidity during the reaction for this reaction product can be compensated by an addition of an organic solvent. However, the addition of the solvent tends to lead to a decrease in the productivity due to a decrease of the space time yield, and the yield relative to the starting materials tends to decrease. Such should be avoided as far as possible.
The decrease of the fluidity and the decrease of the reaction yield by dilution with a solvent become fatal drawbacks in a case where the reaction for the synthesis of copper phthalocyanine is continuously conducted by a multi tank reaction system, since the transfer of the reaction solution between the tanks at a constant rate can not be expected at all.
Such a high viscosity phenomenon of the reaction solution due to a substantial decrease in the fluidity of the reaction product during the reaction for the synthesis of copper phthalocyanine is believed to cause non-uniformity in the reaction temperature distribution in the reaction product, since the reaction for the formation of copper phthalocyanine in the urea method is an endothermic reaction of about 80 kcal/mol and the activation energy is fairly large at a level of about 40 kcal/mol. It is believed that this brings about non-uniformity in the partial reaction rate in the reaction product, prevents the reproducibility of the reaction and causes the decrease in the reaction yield and a deterioration in the quality of the pigment as a final product.
Thus, the low fluidity due to the high viscosity of the reaction solution as time passes during the production of copper phthalocyanine by the urea method, brings about a decrease in the yield of the product (crude pigment which may be called non-pigmented crude or simply crude) and a deterioration in the quality of the pigment obtained. Further, it presents a fatal defect in the continuous operation of the reaction for the synthesis of copper phthalocyanine.
As a method for solving the problem of the conventional urea method as described above, there has been recently proposed a method wherein a large amount of solvent is used for the reaction and at the same time the agitation is enhanced, or a method wherein a surface active agent is added to the reaction mixture, for example, in Japanese Unexamined Patent Publication Nos. 10659/1987 and 10660/1987. However, the former method has a problem that it is industrially disadvantageous since the space time yield decreases, and the latter method has a problem that the surface active agent added at the time of the reaction is included dee in the formed copper phthalocyanine crystals, so that it is difficult to completely remove such surface active agent even in the subsequent purification step, and such a surface active agent is likely to substantially deteriorate the performance of a printing ink prepared by using such copper phthalocyanine.
It is an object of the present invention to solve all such conventional problems as described above and to provide novel process whereby crude metal phthalocyanines of high purity with high performance can be prepared in good yield industrially advantageously, either by the so-called urea method or the phthalodinitrile method.